Most asphalt paving machines are of the "floating screed" type in which asphaltic material is distributed in front of a screed as the paver is moved over the ground. The screed floats on the asphalt and compresses the asphalt material into a mat. The texture and density of the asphalt mat are influenced by a number of factors, including the weight of the screed assembly and the angle of the screed assembly relative to the ground. Some screed assemblies also include a rotating shaft, having a series of counterweights, which vibrates the screed and further compacts the asphalt.
The width of the asphalt mat is generally limited to the width of the paving machine, although in some instances the width may be increased by using extended screeds. Nevertheless, in most paving applications, such as two lane roadways, the paver must make at least two passes. When paving wider roads or parking lots, the paver must typically make a number of passes in order to apply an asphalt mat of the desired width. Each time the paver makes an additional pass, a longitudinal joint is created between the two passes. Unfortunately, these longitudinal joints are frequently the first point of failure.
The edges of the pavement mat, especially the edges of the first pass, are usually less compacted than the center section due to the fact that the edges are generally unconfined as the asphalt is applied. These low density areas may include air voids and are especially vulnerable to the ingress of water and/or road salt, all of which leads to degradation of the joint and eventual pavement failure. In some circumstances the edge of the pavement will collapse under the weight of the compacting roller, especially when the edge is unconfined. Poor longitudinal joint quality is the most frequent cause of expensive repairs, and in many instances repair may not be feasible and the entire application must be re-paved.
Accordingly, there exists a need to improve compaction of the asphalt mat, with special focus on the edge of the mat, in order to reduce the occurrence of longitudinal joint failure.